Refrigerant system with multi-speed scroll compressor and economizer circuit

ABSTRACT

A scroll compressor is provided with a multiple-speed motor. A control selects a speed for operating the motor, along with selecting between several available options for the system capacity adjustment to meet external load demands in a most efficient and reliable manner. The disclosed embodiment includes an economizer circuit, an unloader function, and an optional suction modulation valve. By utilizing each of these features in combination with the multi-speed motor for the compressor, the present invention is better able to tailor provided capacity to desired capacity.

BACKGROUND OF THE INVENTION

This invention relates to a two-speed scroll compressor that is operablein a refrigerant system with an economizer function and other means ofcapacity modulation.

Refrigerant systems are utilized in many applications to condition anenvironment. In particular, air conditioners and heat pumps are employedto cool and/or heat a secondary fluid such as air entering anenvironment. The cooling or heating load of the environment may varywith ambient conditions, occupancy level, other changes in sensible andlatent load demands, and as the temperature and/or humidity set pointsare adjusted by an occupant of the building.

Thus, refrigerant systems can be provided with sophisticated controls,and a number of optional components and features to adjust coolingand/or heating capacity. Known options include the ability to bypassrefrigerant which has been at least partially compressed by a compressorback to a suction line. This function is also known as an unloaderbypass function. This additional step in operation is taken to reducesystem capacity.

Another option includes a so-called economizer cycle. In an economizercycle, a main refrigerant flow heading to an evaporator is subcooled inan economizer heat exchanger. The main refrigerant flow is subcooled bya tapped refrigerant that is expanded to some intermediate pressure andtemperature levels and then passed through the economizer heatexchanger. This tapped refrigerant is then returned to a compressor atan intermediate point in the compression cycle. Thus, the economizercycle provides an additional step in operation to vary system capacityby switching between economized and other modes (or steps) of operation.

In the prior art, controls can be programmed to optionally actuate anyone of these various control functions. However, the capacity providedby these functions is increased or decreased in relatively largediscrete steps. It would be desirable to provide the ability to vary thecapacity while the system is running at any of the above described modesof operation, in order to more closely match external load demands.

Motor drives are known for driving compressors at two speeds in arefrigerant system. By driving the compressor at a higher or lowerspeed, the amount of refrigerant that is compressed and circulatedthroughout the system changes, and thus the system capacity can bechanged accordingly.

One increasingly popular type of compressors is a scroll compressor. Ina scroll compressor, a pair of scroll members orbits relative to eachother to compress an entrapped refrigerant. One design configuration ofa scroll compressor utilizes both economizer and various unloaderfunctions. Further, this scroll compressor may employ a singleintermediate port to provide both functions alternatively orsimultaneously. This scroll compressor is disclosed in U.S. Pat. No.5,996,364.

However, scroll compressors have not been utilized in combination with atwo-speed drive for its motor and an economizer cycle to obtainadditional flexibility in system operation and control.

SUMMARY OF THE INVENTION

In a disclosed embodiment of this invention, a scroll compressor isprovided in a refrigerant system with an economizer circuit. The scrollcompressor has a motor that can be driven at multiple discreet speeds.For illustration purposes, the discussion below deals with a two-speedmotor. However, the scroll compressor can be run at more than twodistinct speeds. By selectively utilizing the economizer circuit, and/oran optional unloader function, the controller can increase or decreasethe capacity of the refrigerant system. Further, by varying the speed ofthe motor, system capacity within each mode of operation can be adjustedto provide additional control flexibility.

A controller identifies a desired capacity level, and then achieves thisdesired capacity level by actuating the economizer circuit, if increasedcapacity is desired, or not actuating the economizer cycle if extracapacity is not required, or providing additional means of unloading toreduce the capacity even further, and determining a desired motor speedfor achieving the exact capacity level. Since the refrigerant compressorprovides efficient and reliable operation only within a certain speedrange, additional steps of capacity correction, such as the unloaderfunction, with or without the economizer circuit engaged, may be desiredand similarly utilized with the corresponding compressor motor speedadjustment to closely control the capacity level or achieve moreefficient unit operation. Additionally, the controller may monitor thesystem efficiency level and select the most desirable mode of operationand motor speed. In this case, both capacity and efficiencyconsiderations are taken into account to establish the optimum unitoperation.

By providing the two-speed drive in combination with the capacityadjustment options mentioned above, the present invention allows an enduser to closely tailor the system capacity and/or efficiency, or acombination of these two parameters, to a desired level. As also known,an additional throttling device, often called a suction modulation valve(SMV) may be provided to further reduce the capacity to the level belowthe level that would be normally achievable through the unloadingmechanisms and reduction in motor speed.

These and other features of the present invention can be best understoodfrom the following specification and drawings, the following of which isa brief description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a first embodiment refrigerant cycle.

FIG. 1B is another embodiment.

FIG. 2A shows a graph of the capacity provided by the prior art.

FIG. 2B shows a graph of the capacity provided by the invention.

FIG. 3 is a flow chart.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A refrigerant system 20 is illustrated in FIG. 1A having a compressor 22and a controller 44. As is known, a motor 24 for the compressor 22 canbe driven at two speeds such that the amount of refrigerant compressedand circulated throughout the system by the compressor 22 can be varied.That is, the compressor can be driven at one of two non-zero speeds atsteady state operation. The compressor 22 is a scroll compressor havingan orbiting scroll member 26 and a non-orbiting scroll member 28. As isknown, a number of compression chambers are defined between the twoscroll members to compress an entrapped refrigerant when the orbitingscroll member 26 is driven to orbit by the electric motor 24. As can beseen, a suction tube 30 leads refrigerant into a suction chamber 31surrounding the motor and leading into the compression chambers. Oncethe refrigerant is compressed, it is driven into a discharge chamber 33communicating with a discharge port 32. The general structure of ascroll compressor is known. As also shown, an injection line 34, to bedisclosed below, communicates with a port (or ports) 51 that ispositioned at an intermediate compression point.

Refrigerant compressed by the compressor 22 is discharged from thedischarge port 32, and then to an outdoor heat exchanger 46, which wouldbe the condenser in a cooling mode. Fan 47 moves air over the heatexchanger 46. Downstream of the condenser 46 is an economizer heatexchanger 48. The economizer heat exchanger 48 may be a conventionalheat exchanger or may be of a flash tank type. As is known, theeconomizer heat exchanger receives a tapped refrigerant from a tap line45 passing through an economizer expansion device 49, and a mainrefrigerant from a liquid line 41. Although the two refrigerant streamsare shown flowing in the same direction in FIG. 1, this is merely tosimplify the illustration. In practice, it is generally preferred tohave the two flows flowing in a counterflow arrangement.

The tapped refrigerant in the tap line 45 subcools the refrigerant inthe liquid line 41, such that after passing through a main expansiondevice 52, it will have a higher cooling potential prior to entering anevaporator 54. Fan 55 moves air over the evaporator 54. From theevaporator 54, the refrigerant returns to a suction line 30 leading backto the compressor 22. An optional suction modulation valve 61 can bepositioned in the suction line 30 between the compressor 22 andevaporator 54. The tapped refrigerant from the tap line 45 passesthrough the return injection line 34 to enter the intermediatecompression point or injection port (or plurality of ports) 51 in thecompressor 22. A bypass line 19 may selectively bypass refrigerant fromthe compressor 22 back to the suction line 30 when a bypass valve 40 isopened. It should be understood that the economizer expansion device 49also preferably incorporates a shutoff feature, or a separate shutoffdevice 36 is provided. When the bypass valve 40 is opened, the shutoffdevice 36 is preferably closed, and when the shutoff device 36 isopened, the bypass valve 40 is typically closed; however, it is alsopossible to operate with both shutoff valve 36 and bypass valve 40 open.As shown, the same port of the injection line 34 can be used to deliverthe refrigerant from the economizer heat exchanger as well as to bypassthe refrigerant back to the suction line. Of course, if so desired, thebypass and refrigerant injection functions can utilize different ports,instead of the common port 51.

As is known, the bypass valve 40 is opened when part-load capacity ofthe compressor 22 is desirable. Thus, partially compressed refrigerantis returned to the suction line 30, and the cooling capacity of therefrigerant system is reduced. If a capacity increase is desired, thenthe bypass valve 40 is closed. If even further capacity augmentation isdesired, then the bypass valve 40 is closed and the economizer expansiondevice 49 (or shutoff device 36) is opened to provide the economizerfunction. An enhanced capacity is then provided.

A control 44 for refrigerant cycle 20 is able to identify a desiredcooling capacity, and operate the bypass function and/or the economizerfunction as necessary. Thus, as shown in FIG. 2A, the prior art systemprovides varying stages of capacity. One stage corresponds to operationin the economized mode; another stage corresponds to operation in theeconomized and bypass modes engaged at the same time; still anotherstage corresponds to non-economized mode; and yet another stagecorresponds to the bypass mode of operation. If there is an additionalSMV present, then, as shown, by throttling the SMV between the modes ofoperation mentioned above the capacity can be adjusted between thesemodes. However, the SMV operation is inefficient, and in general shouldbe avoided if possible.

When the system of FIG. 1A includes a two-speed compressor motor, thenthere can be additional capacity control between the base values, withor without the use of SMV. Thus, as shown in FIG. 2B, if the system wasoperating at maximum capacity at point E1 (which would normallycorrespond to economized circuit engaged and the compressor running at amaximum speed) by reducing the speed of the compressor the capacity canbe reduced to point E2. If further reduction is desired the compressorspeed is adjusted and the switch is made to the economized mode with oneof the available unloader option (for instance, bypass) engaged.

The control 44 controls each of these options and changes the speed (seeFIG. 3) of the compressor motor between the two available speeds toachieve a capacity, which closely matches the needed capacity. Althoughthe control can change mode or speed under any algorithm that maydetermine the most desired operation, the mostly preferred control logicwould be based on efficiency and reliability considerations. The presentinvention is thus able to better tailor the provided capacity to therequired capacity to meet external load demands by utilizing each ofthese several options.

FIG. 1B shows another embodiment, wherein the compressor 122 is shownschematically, but wherein the economizer injection line 134 and theunloader line 136 communicate with distinct ports in the compressor 122.This figure shows this feature somewhat schematically (note that suctionand discharge port of the compressor 122 are not exhibited), but aworker of ordinary skill in the art would recognize how, to achieve thisstructure.

In further aspects, it is known to make the economizer and unloaderfunctions continuously adjustable. Still, providing a two-speedcompressor will allow even more flexible, reliable and efficientoperation to be achieved. Also, as mentioned above, a multi-speed motor(in place of a two-speed motor) can be incorporated intro the compressordesign to provide an additional degree of flexibility.

Although a preferred embodiment of this invention has been disclosed, aworker of ordinary skill in this art would recognize that certainmodifications would come within the scope of this invention. For thatreason, the following claims should be studied to determine the truescope and content of this invention.

1. A refrigerant system comprising: at least one compressor having amulti-speed drive for providing multiple speeds for said compressor, andsaid compressor being provided with a suction port, an intermediatepressure port and discharge port; a condenser downstream of saidcompressor, a main expansion device downstream of said condenser, anevaporator downstream of said main expansion device, with an economizercircuit containing an economizer expansion device and an economizer heatexchanger and positioned intermediate to said condenser and saidevaporator, said economizer circuit selectively returning a tappedrefrigerant to said compressor; a control for selectively operating saideconomizer circuit to deliver a tapped refrigerant through saideconomizer heat exchanger, and back to said compressor, and said controlalso selecting a speed of said compressor to achieve various levels ofcapacity, said control being programmed to select between availablemodes of operation, said available modes of operation including at leastoperation with said economizer circuit operational, and without saideconomizer circuit operational, and said control first selecting a modeto best achieve desired conditions for an environment to be conditioned,then varying a speed of the motor if further variation is required tomeet the desired conditions; and there is a suction modulation valvelocated downstream of said evaporator and its operation is one of themodes of operation.
 2. The refrigerant system as set forth in claim 1,wherein a multi-speed drive is a two-speed drive.
 3. The refrigerantsystem as set forth in claim 1, wherein said compressor is a scrollcompressor.
 4. The refrigerant system as set forth in claim 1, whereinsaid tapped refrigerant is returned to said intermediate compressionport.
 5. The refrigerant system as set forth in claim 1, wherein thedelivery of said tapped refrigerant is controlled by a flow controldevice.
 6. The refrigerant system as set forth in claim 1, wherein saidcontrol operates under an operational mode sequence to utilize themulti-speed drive and the economizer circuit based on efficiency andreliability considerations.
 7. A refrigerant system comprising: at leastone compressor having a multi-speed drive for providing multiple speedsfor said compressor, and said compressor being provided with a suctionport, an intermediate pressure port and discharge port; a condenserdownstream of said compressor, a main expansion device downstream ofsaid condenser, an evaporator downstream of said main expansion device,with an economizer circuit containing an economizer expansion device andan economizer heat exchanger and positioned intermediate to saidcondenser and said evaporator, said economizer circuit selectivelyreturning a tapped refrigerant to said compressor; a control forselectively operating said economizer circuit to deliver a tappedrefrigerant through said economizer heat exchanger, and back to saidcompressor, and said control also selecting a speed of said compressorto achieve various levels of capacity, said control being programmed toselect between available modes of operation, said available modes ofoperation including at least operation with said economizer circuitoperational, and without said economizer circuit operational, and saidcontrol first selecting a mode to best achieve desired conditions for anenvironment to be conditioned, then varying a speed of the motor iffurther variation is required to meet the desired conditions; andwherein a bypass port is also provided for said compressor toselectively bypass at least a portion of partially compressedrefrigerant from said compressor back to a suction line for saidcompressor and its operation is one of the available modes.
 8. Therefrigerant system as set forth in claim 7, wherein said bypass port andsaid intermediate pressure port are provided by the same port.
 9. Therefrigerant system as set forth in claim 8, wherein said bypass portselectively communicates an intermediate pressure line receiving saidtapped refrigerant back to a suction line leading to said compressor.10. The refrigerant system as set forth in claim 7, wherein the deliveryof said bypass refrigerant is controlled by a flow control device.
 11. Amethod of operating a refrigerant system having at least one multi-speedcompressor and at least one economizer circuit; first determining adesired load on said refrigerant system, and determining whether saideconomizer circuit should be engaged to meet said desired load or shouldbe left off as possible modes of operation; then varying a speed of saidcompressor to meet said desired load if further variation is required tomeet the desired conditions; and wherein said compressor is furtherprovided with an unloader function, and both said unloader function andsaid economizer circuits providing modes to meet said desired load. 12.The method as said forth in claim 11, wherein the multi-speed compressoris a two-speed compressor.
 13. The method as set forth in claim 11,wherein a control operates said economizer circuit and said multi-speedcompressor utilizing an operation mode sequence based upon efficiencyand reliability considerations.
 14. A method of operating a refrigerantsystem having at least one multi-speed compressor and at least oneeconomizer circuit; first determining a desired load on said refrigerantsystem, and determining whether said economizer circuit should beengaged to meet said desired load or should be left off as possiblemodes of operation; then varying a speed of said compressor to meet saiddesired load if further variation is required to meet the desiredconditions; and wherein a suction modulation valve is also provided, andis actuated as one of the modes to vary the operational function of therefrigerant system to meet said desired load.